Allow mipscalls to change the return value.

At least, seems like mpeg needs this.
Move Action out of Common, don't use savedV0.

Compiler error was annoying me anyway.
Mpeg timestamps are in the wrong dword order.
Notice the end of video and error appropriately.
Enable fake mpeg mode by default.

Note: loaded save states will have it off.  No UI yet.
Fake the audio timestamp, games check it.
Merge pull request #348 from unknownbrackets/mpeg-fix

Fix games broken by the mpeg merge